Motor control circuit

ABSTRACT

A remote-controlled vehicle has left and right driving wheels independently propelled by a pair of DC electric motors, with the vehicle being responsive to a control signal transmitted by a portable transmitter carried by a moving individual for transporting a load at a predetermined distance behind said individual. The vehicle has an improved electronic control system comprising a receiver for receiving the transmitted control signal and developing therefrom a range signal representative of the distance between the individual and the vehicle and a bearing signal representative of the heading of the vehicle relative to said individual. A DC amplifier circuit converts the bearing and range signals to left and right DC control signals. An astable multivibrator generates a pair of fixed-frequency pulse-train signals which are each converted to trapezoidal pulse-train signals by an integrating circuit. The left and right DC control signals are combined with the trapezoidal pulse-train signals and are applied to a threshold switching circuit which develops a variable-width rectangular pulse-train signal which is applied to the motor.

ited States Patent 1 Ohba [451 July 24, 1973 1 MOTOR CONTROL CIRCUIT[76] Inventor: Shunjiro Ohba, 5969 N. Elston Ave., Chicago, 111. 60646[22] Filed: July 7, 1972 [21] Appl. No.: 269,743

[52] US. Cl 318/587, 318/16, 180/65 [51] Int. Cl G05d 1/00, B64c 16/18 v[58] Field of Search 318/16, 587; 180/65 [56] References Cited UNITEDSTATES PATENTS 2,892,290 6/1959 Ryan 318/16 X 3,009,271 11/1961 Kuehneet al....... 318/587 X 3,303,821 2/1967 Harris l80/6.5

3,374,845 3/1968 Selwyn 318/16 X Prima y Examiner-B. DobeckAttorney-William E. Anderson et a1.

[57] ABSTRACT A remote-controlled vehicle has left and right drivingMATE/X AM/Z/HER wheels independently propelled by a pair of DC electricmotors, with the vehicle being responsive to a control signaltransmitted by a portable transmitter carried by a moving individual fortransporting a load at a predetermined distance behind said individual.The vehicle has an improved electronic control system comprising areceiver for receiving the transmitted control signal and developingtherefrom a range signal representative of the distance between theindividual and the vehicle and a bearing signal representative of theheading of the vehicle relative to said individual. A DC amplifiercircuit converts the bearing and range signals to left and right DCcontrol signals. An astable multivibrator generates a pair offixed-frequency pulse-train signals which are each converted totrapezoidal pulsetrain signals by an integrating circuit. The left andright DC control signals are combined with the trapezoidal pulse-trainsignals and are applied to a threshold switching circuit which developsa variable-width rectangular pulse-train signal which is applied to themotor.

6 Claims, 4 Drawing Figures 1 LEFT MOTOR CONTROL CIRCUIT The presentinvention generally relates to remotecontrolled motor-driven vehiclesand, more particularly, to a DC motor control circuit for such avehicle.

Motor-driven vehicles suitable for transporting a load of some sort andfollowing a moving individual at a prescribed distance are known. Oneparticular application for such a vehicle is a three-wheeled cart forcarrying a golfers golf bag, clubs, etc. The golfer carries a smallradio transmitter in his pocket which transmits a control signal to areceiver in the cart so that, ideally, the cart follows the golferaround the golf course at a distance of approximately seven feet withouteither overrunning the golfer or falling too far behind him. Such cartsare often used in preference to riding carts be-' cause they enable somegolfers to enjoy the benefits of the exercise involved in walkingaroundthe golf course without suffering the burden of carrying a heavybag of golf clubs and other equipment which may tend to tire the golferand have an adverse affect on his playing ability.

Such carts are commonly driven by one or more DC motors which arepowered by rechargeable storage batteries. Typically, a pair of antennasand a control circuit are employed to cause the cart to sense theintensity and relative direction of the transmitted signal to developbearing and range control signals which are ultimately applied to thedriving motor(s) to maintain the vehicle at the desired distance behindthe golfer. Motors commonly used for such vehicles are relativelylow-voltage (e.g., 12 volts), high current (e.g., I amps) devices;consequently, a DC amplifier is often employed to amplify the bearingand range control signals to a level suitable for application to themotors. Rheostats or variable resistors could be used to control themotors but such would result in lost power in terms of the energydissipated in the resistance. Conventional circuits for controlling thedriving motors in response to the bearing and range signals, however,are often inefficient and sluggish in that they consume a relativelylarge amount of power and do not precisely control the movement of thevehicle, especially when it is moving downhill. i v

Accordingly, it is an object of the present invention to provide animproved electronic DC motor control system for a remote-controlled,motor-driven vehicle of the type suitable for automatically transportinga load at a predetermined distance behind a walking individual.

It is another object of the invention to provide such a system whichincreases .the efficiency of the vehicle and controls the DC motors moreprecisely than systems heretofore used.

Other objects and advantages of the invention are more particularly setforth in the following detailed description, and in the accompanyingdrawings, of which:

FIG. 1 is a perspective view of a vehicle constructed in accordance withthe invention;

FIG. 2 is a perspective view of the veicle shown in FIG. 1 but with theouter portion removed to show the internal construction of the vehicle;

FIG. 3 is an electrical schematic diagram of a control circuitconstructed in accordance with the principles of the invention andsuitable for use in the vehicle illustrated in FIGS. 1 and 2; and

FIG. 4 is a graphical representation of the wave forms of some of thesignals in the circuit illustrated in FIG. 3.

With reference to FIGS. 1 and 2, there is generally shown aremote-controlled motor-driven vehicle 10 responsive to a control signaltransmitted by a portable transmitter carried by a moving individual(neither is shown), such as a golfer walking around a golf course, fortransporting a load such asa bag of golf clubs 11 at a predetermineddistance (e.g., about seven feet) behind the individual. As illustrated,vehicle 10 is a typical three-wheeled cart with two rear driving wheels21 and 22 independently propelled by separate DC electric motors M and Mrespectively, which are powered by a rechargeable storage battery 25.FIG. 2 is a perspective view of vehicle 10 shown in FIG. 1 but with theouter shell or housing 12 removed. A single front wheel 13 is madefreely pivotable about a substantially vertical axis so that thevehiclemay be steered by applying. greater power to one rear wheel than to theother so as to turn the vehicle in a manner similar to that of a tracktype vehicle, such as an armored tank. The particular way in which themotors are coupled to the wheels forms no part of the invention and thusmay be carried out in any suitable manner including a gear train,driving chain, orthe like. A pair of antennas 30, 35 are provided forreceiving the transmitted control signal and applying a correspondingelectrical signal to electronic control circuitry contained in a housing20 and discussed .in greaterdetail below with reference-to FIG. 3. a

The transmitter used in conjunction with the system of the invention maybe of any conventional type suitable for developing a control signal andpropagating it a distance of up to 25 feet or so, depending on theparticular circumstances in which the invention is used. The transmitteris preferably a small portable device which may be conveniently carriedby the individual in his pocket or on his belt, etc. The transmittershould also have an on/off switch so that the individual may disablethe-remote-control system when, for example, he wishes to move closeenough to the cart (i.e., with the aforementioned ten-foot followingdistance) to select a club, or while he is off the course such as whenhe is searching for a lostball. The signalradiated by the transmittermay preferably "be magnetic, rather than electromagnetic, so as to havea limited radiation range, similar to the signals radiated in somegarage door opening systems or the like. Moreover, increased immunity ofthe control system to extraneous signals may be achieved by utilizing anRF carrier wave signal modulated with a predetermined tone signal andemploying circuitry to-detect both the carrier frequency and themodulation frequency. Thus, an extraneous signal having a component atthe carrier frequency with an amplitude large enough to be detected bythe control system will not actuate it. Carrier wave control signals ofdifferent frequencies may be used to enable each member of a group ofgolfers, for example, to use such a vehicle.

With reference to FIG. 3, there is shown an electrical schematic wiringdiagram of a circuit constructed in accordance with the principles ofthe present invention which may be advantageously employed in thevehicle illustrated in FIGS. land 2. In general, the illustratedembodiment of the invention comprises receiving means including antennas30 and 35, RF amplifiers 40 and 45, and demodulators 50 and 55, forreceiving the transmitted signal and developing therefrom a range signalrepresentative of the distance between the individual and the vehicleand a bearing signal representative of the heading of the vehiclerelative to the individual. Means comprising a DC amplifying andmatrixing circuit 60 is responsive to the range and bearing signals fordeveloping left and right DC control signals. Means including left andright threshold switching circuits 70L and 70R, an astable multivibrator75, and a pair of integrating circuits 90L, 90R are responsive to theleft and right DC control signals for developing corresponding left andright pulsed electrical signals each comprising a series of rectangularpulses having a pulse width and polarity that systematically vary inaccordance with amplitude and polarity of the corresponding dc controlignal. The left and right variable-width pulsed signals are respectivelyapplied to left and right motors M L and M by means of two pairs of DCamplifiers 81L, 82L and 81R, 82R.

In accordance with an optional feature of the invention, more effectivemotor control is obtained by using a pair of feedback control circuits1001,, 100 R which integrate the motor voltage signal and apply anegative feedback signal to the input of control circuits 70L and 70R,respectively.

More particularly, the embodiment of the invention illustrated in FIG. 3includes antennas 30 and 35 which may preferably comprise ferrite rods33 and 38, respectively, having wound thereon primary windings 34 and39, respectively, which are each tuned to the frequency of the controlsignal by a suitable capacitor and variable inductor tuning circuit. Therange signal is developed by a pair of secondary windings 32, 36 ofantennas 30, 35, respectively, which are connected together in phase toproduce a signal representative of the sum of the two signals receivedby antennas 30 and 35. The bearing signal is developed by a pair ofsecondary windings 31, 37 of antennas 30, 35 respectively, which areconnected together in phase opposition to develop a signalrepresentative of the difference between the two signals received byantennas 30 and 35. The thusdeveloped AC bearing and range signals areapplied to conventional RF amplifier circuits 40 and 45, respectively(assuming the transmitted control signal has a frequency in the radiofrequency spectrum). RF amplifier circuits 40 and 45 may be of anyconventional design suitable to amplify the AC input signals from eachpair of secondary windings 31, 36 and 32, 37, respectively, to a signallevel suitable for application to demodulator circuits 50 and 55,respectively. Demodulator circuit 50 converts the bearing input signalfrom RF amplifier circuit 40 to a DC bearing signal having an amplituderepresentative of the amount or degree of heading error and having apolarity representative of the relative direction, right or left, of theheading error. For example, the signal from left antenna 30 may be usedas a reference such that, when the individual with the transmitterassociated with vehicle is located to the left of the vehicle, leftantenna receives a stronger or more intense signal than does rightantenna hence, the difference signal applied to RF amplifier has a phasethat is positive." When the individual is located to the right ofvehicle 10, however, left antenna 30 receives a weaker or lessintense'signal than does right antenna 35; hence, the difference signalhas a phase that is-negative. Consequently, a positive DC output signalfrom demodulator 50 may be used to indicate a vehicle heading to theright of the individual; a negative DC output signal, to the left. Thisphasepolarity-direction relationship is arbitrarily chosen and may, ofcourse, be selected in any suitable manner. Similarly, demodulatorcircuit 55 converts the AC range input signal from RF amplifier 45 to aDC range signal having an amplitude representative of the distance fromthe vehicle to the individual. The RF amplifier and demodulators per se,of the control system form no part of the invention and, if desired,this portion of the system may further include various design featuressuch as automatic gain control (AGC), buffering, or limiting.

In the specific embodiment of the invention illustrated in FIG. 3, theDC output signals from demodulators 50 and 55 are coupled to a DCamplifier and matrix circuit 60 wherein the range (sum) and bearing(difference) signals are converted into left and right control signalswhich are respectively applied to left and right threshold switchingcircuits L and 70R to ultimately control left and right motors M and MOther embodiments of the invention may, of course, include differentarrangements for utilizing the range and bearing signals to control thevehicle. For example, the bearing signal may be used to control theorientation of front wheel 13 of vehicle 10 to thus direct the vehiclein the desired direction and the range signal used to control both rearwheels 21 and 22 to control the speed of the vehicle to thus maintainthe desired distance between the vehicle and the individual it isfollowing. Another example is one in which the front wheel is used forboth steering and driving the vehicle, similar to a front-wheel-driveautomobile.

DC amplifier and matrix circuit 60 may comprise conventional circuitryincluding, for example, a plurality of operational amplifiers (notshown) which both amplify the input DC bearing and range signals andmatrix or cross-couple them such that the DC output signals of circuit60 are in the form of left" and right DC control signals which may beutilized to control left and right motors M and M to control the speedand direction of the vehicle.

At this point it is convenient to note that if identical motors andcoupling mechanisms are used for left wheel 21 and right wheel 22, thenin order to drive the vehicle forward in a straight line it is necessaryto apply equal-amplitude but opposite-polarity control signals to motorsM and M This is due to the fact that the motors are generally moreconveniently mounted with their output driving shafts facing in oppositedirections, as shown in FIG. 2. Thus, assuming that the bearing signalis zero, DC amplifying and matrixing circuit 60 develops left" andright" DC control signals of equal amplitude but opposite polarity.Consequently, motors M and M are driven at the same speed but inopposite directions so that the vehicle moves forward in a straightline. On the other hand, assuming that the range signal is zero, circuit60 develops left and right" DC control signals of equal amplitude andthe same polarity. Consequently, motors M and M are driven at the samespeed and in the same direction so that the vehicle turns. When neitherthe range nor the bearing signal is zero, the left" and right controlsignals represent the cumulative effect of the two input signals suchthat the vehicle may be simultaneously turned and moved toward theindividual. The vehicle moves forward as long as it is not within apredetermined range (e.g., 7 feet) and turns according to the relativevalues of the left and right DC control signals. For example, thevehicle may be turned to the left when the value of the left" controlvoltage is more positive than that of the right, and to the right whenthe value of the left control voltage is more negative than that of theright." Thus, for example, if the range signal indicates that thevehicle should move closer to the individual and the bearing signalindicates that the vehicle should turn to the left in order to move in adirection toward the individual, then both motors M and M B would beactuate but right motor M R would initially be driven harder than leftmotor M so that the vehicle would both align itself in a directiontowards the individual and move in that direction.

In accordance with the illustrated embodiment of the invention,threshold switching circuits 70L and 70R are responsive to the left andright DC control signals and the output signals from integratingcircuits 90L and 90R for respectively developing the left and rightpulsetrain electrical signals which are applied to DC amplifiers 81L,82L, 81R, and 82R. The construction and operation of switching circuit70L, DC amplifiers 81L and 82L, integrating circuit 90L, feedbackcircuit 100L, and motor M is essentially identical to that of switchingcircuit 70R, DC amplifiers 81R and 82R, integrating circuit 90R,feedback circuit 100R, and motor M so only the latter is described indetail. Astable multivibrator 95 is a conventional circuit comprising apair of switching transistors 96,97 and associated biasing and timingcircuitry for generating a pair of rectangular pulse-train signals (FIG.4a) having a constant repetition rate and uniform pulse width which areapplied to integrating circuits 90L and 90R.

Integrating circuit 90R changes the rectangular pulse-train signal frommultivibrator 95 to a trapezoidal pulse-train signal (FIG. 4b) which itapplies to the input of threshold switching circuit 70R. The right DCcontrol signal (level 401 in FIG. 4c) is also applied to the input ofthreshold switching circuit 70R to thus determine the DC level of thetrapezoidal pulse-train signal. It should be noted that it is notessential to use a signal having a trapezoidal waveform; any periodicsignal having sloping leading and trailing edges for each cycle issuitable for the purposes of the invention (e.g., a triangularwaveform).

Threshold switching circuit 70R comprises four switching transistors 71,72, 73 and 74 and the associated biasing circuitry which respond to thetrapezoidal pulse-train signal exceeding a predetermined positivevoltage level to produce an output signal which is applied to DCamplifier 81R. When the trapezoidal pulsetrain signal falls below thepredetermined positive voltage level, no output signal is produced.Thus, by selecting a threshold switching level (level 402 of FIG. 4c)that occurs somewhere on the slanted leading and trailing edges or theslopes" of the trapezoidal waveform, the trapezoidal pulse-train signalis converted to a positive rectangular pulse-train signal which isapplied to motor M by means of DC amplifier 81R. By utilizing the rightDC control signal to vary the DC level of the trapezoidal pulse-trainsignal, the point on the trapezoidal slopes that is equal to thethreshold switching voltage is correspondingly varied to thus produce aconstant-amplitude rectangular output signal having a pulse width thatvaries in accordance with the right DC control signal. If, at time t inFIG. 4, the right DC control voltage changes to a different level (level403 in FIG. 4c), then the points on the slopes of the waveformcorresponding to detection or threshold level 402 changes to produce awider pulse, as shown in FIG. 4d. Threshold switching circuit R ismade-symmetrical by including four complementery switching transistors76, 77, 78, and 79 and the associated biasing circuitry to respond to acorresponding predetermined negative threshold voltage tosimilarly applya negative rectangular pulse-train signal to motor M by means of DCamplifier 82R. Motor M is thereby driven at a torque corresponding tothe width of the rectangular driving pulses and in a directioncorresponding to the polarity of the pulses.

In accordance with an optional aspect of the illustrated embodiment ofthe invention, a feedback control circuit R is provided to improve theoperation characteristics of the motor control circuit. Feedback controlcircuit 100R includes an operational amplifier 10] having a feedbackcircuit comprising a resistor 102 and a capacitor 103 for integratingthe signal appearing at the input terminal of motor M (a voltagecomprising the combination of the applied pulse-train signal plus theemf of the motor) and applying a corresponding DC signal to the input ofthreshold switching circuit 70R. This causes motor M to operate in aspeed controlled mode rather than torque controlled mode used inconventional controllers. In addition, the circuit provides dynamicbraking when the range control signal decreases the motor speed.Moreover, when the vehicle is moving in a downhill manner, the circuitof the invention provides more efficient braking even when the vehiclechanges its heading.

Thus there has been shown and described an improved electronic DC motorcontrol system for a remote-controlled, motor-driven vehicle of the typesuitable for automatically transporting a load at a pre determineddistance behind a walking individual. By developing a train ofvariable-width, constantamplitude pulses to control the DC motors of thevehicle, minimum power is lost in rheostats or other powerconsumingdevices used to control the torque output of the motors. Moreover, byintegrating the input signal to the motors (plus the motor emf) anddeveloping a corresponding DC signal which is applied to the input ofthe motor control circuits, thus R.P.M. control and dynamic braking isobtained.

It will, of course, be understood that modifications of the presentinvention, in its various aspects, will be apparent to those skilled inthe art, some being apparent only after study, and others being merelymatters of routine design. As such, the scope of the invention shouldnot be limited by the particular embodiment and specific constructionherein described, but should be defined only by the appended claims, andequivalents thereof.

Various features of the invention are set forth in the following claims.

What is claimed is:

1. In a remote-controlled vehicle having left and right driving wheelsindependently propelled by a pair of DC electric motors, said vehicleresponsive to a control sig nal transmitted by a portable transmittercarried by a moving individual for transporting a load at apredetermined distance behind said individual, an improved electroniccontrol system comprising:

means for receiving said transmitted control signal and developingtherefrom a range signal representative of the distance between saidindividual and said vehicle and a bearing signal representative of theheading of said vehicle relative to said individual;

means responsive to said range and bearing signals for generatingrespective left and right pulse-train electrical signals each comprisinga series of pulses having a pulse width and polarity that systematicallyvary in accordance with the range and bearing signals;

and means for applying said left pulse-train electrical signal to themotor propelling said left driving wheel and said right pulse-trainelectrical signal to the motor propelling said right driving wheel.

2. A system according to claim 1, which further comprises meansresponsive to said range and bearing signals for developing a left DCcontrol signal and a right DC control signal, and said generating meansis responsive to said left and right DC control signal for generatingsaid respective left and right pulse-train signals each comprising aseries of rectangular pulses having a pulse width and polarity thatsystematically vary in accordance with the amplitude and polarity of thecorresponding DC control signal.

3. A system according to claim 2, in which said generating meanscomprises means for generating a pair of trapezoidal pulse-train signalshaving DC voltage levels that systematically vary in accordance withsaid left and right DC control signals, respectively, and a thresh oldswitching means responsive to a predetermined threshold switchingvoltage for generating said left and right pulse-train signals.

4. A system according to claim 3, in which said trapezoidal pulse-traingenerating means comprises an astable multivibrator for generating apair of rectangular pulse-train signals, and a pair of integratingcircuits coupled to said multivibrator for converting said rectangularpulse-train signals into said pair of trapezoidal pulse-train signals.

5. A system according to claim 2, which further comprises a pair offeedback control circuits coupled from said motors to said generatingmeans for applying a DC signal to said generating means representativeof the operating characteristics of the respective one of said motors,thereby providing improved motor speed control.

6. A system according to claim 5, in which each said feedback controlcircuit comprises an integrating circult.

1. In a remote-controlled vehicle having left and right driving wheelsindependently propelled by a pair of DC electric motors, said vehicleresponsive to a control signal transmitted by a portable transmittercarried by a moving individual for transporting a load at apredetermined distance behind said individual, an improved electroniccontrol system comprising: means for receiving said transmitted controlsignal and developing therefrom a range signal representative of thedistance between said individual and said vehicle and a bearing signalrepresentative of the heading of said vehicle relative to saidindividual; means responsive to said range and bearing signals forgenerating respective left and right pulse-train electrical signals eachcomprising a series of pulses having a pulse width and polarity thatsystematically vary in accordance with the range and bearing signals;and means for applying said left pulse-train electrical signal to themotor propelling said left driving wheel and said right pulse-trainelectrical signal to the motor propelling said right driving wheel.
 2. Asystem according to claim 1, which further comprises means responsive tosaid range and bearing signals For developing a left DC control signaland a right DC control signal, and said generating means is responsiveto said left and right DC control signal for generating said respectiveleft and right pulse-train signals each comprising a series ofrectangular pulses having a pulse width and polarity that systematicallyvary in accordance with the amplitude and polarity of the correspondingDC control signal.
 3. A system according to claim 2, in which saidgenerating means comprises means for generating a pair of trapezoidalpulse-train signals having DC voltage levels that systematically vary inaccordance with said left and right DC control signals, respectively,and a threshold switching means responsive to a predetermined thresholdswitching voltage for generating said left and right pulse-trainsignals.
 4. A system according to claim 3, in which said trapezoidalpulse-train generating means comprises an astable multivibrator forgenerating a pair of rectangular pulse-train signals, and a pair ofintegrating circuits coupled to said multivibrator for converting saidrectangular pulse-train signals into said pair of trapezoidalpulse-train signals.
 5. A system according to claim 2, which furthercomprises a pair of feedback control circuits coupled from said motorsto said generating means for applying a DC signal to said generatingmeans representative of the operating characteristics of the respectiveone of said motors, thereby providing improved motor speed control.
 6. Asystem according to claim 5, in which each said feedback control circuitcomprises an integrating circuit.